U.S. patent number 5,508,016 [Application Number 08/219,875] was granted by the patent office on 1996-04-16 for process for production of transition alumina.
This patent grant is currently assigned to Sumitomo Chemical Co., Ltd.. Invention is credited to Seiichi Hamano, Osamu Yamanishi.
United States Patent |
5,508,016 |
Yamanishi , et al. |
April 16, 1996 |
Process for production of transition alumina
Abstract
There is provided a process for the production of a transition
alumina by thermally decomposing an aluminum sulfate wherein the
thermal decomposition is carried out under an atmosphere comprising
a reducing substance, and the transition alumina produced by the
process has a specific BET surface are of not smaller than 400
m.sup.2 /g.
Inventors: |
Yamanishi; Osamu (Niihama,
JP), Hamano; Seiichi (Niihama, JP) |
Assignee: |
Sumitomo Chemical Co., Ltd.
(Osaka, JP)
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Family
ID: |
18281745 |
Appl.
No.: |
08/219,875 |
Filed: |
March 30, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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991753 |
Dec 17, 1992 |
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Foreign Application Priority Data
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Dec 18, 1991 [JP] |
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3-334834 |
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Current U.S.
Class: |
423/625 |
Current CPC
Class: |
C01F
7/32 (20130101); C01P 2006/12 (20130101) |
Current International
Class: |
C01F
7/00 (20060101); C01F 7/32 (20060101); C01F
007/02 () |
Field of
Search: |
;423/625,137,628 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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576635 |
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May 1959 |
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CA |
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724082 |
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Dec 1965 |
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CA |
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2419544 |
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Jun 1975 |
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DE |
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17-16934 |
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Sep 1942 |
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JP |
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50-21319 |
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Jul 1975 |
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JP |
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60-171220 |
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Sep 1985 |
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JP |
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563636 |
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Aug 1944 |
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GB |
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Other References
Gendai-(Kogyo) Kagaku-Koza 18, Inorganic Synthetic Chemistry II, p.
113 and FIG. 9.42 (no date). .
"Preparation of Catalytically Active .gamma.-Al.sub.2 O.sub.3 from
a Basic Aluminum Succinate Precursor Precipitated from Homogeneous
Solution" by Ch. Sivaraj et al, Applied Catalysts, 24 (1986) 25-35,
no month. .
Ceramics, vol. 24, No. 11, pp. 1042-1043, 1989, no month. .
Chemical Handbook-Applied Chemistry II (Materials), 3rd Edition, p.
865 and Table 11.25, no date. .
"Formation Process of Alumina by Thermal Decomposition of Aluminum
Sulfate" by S. Kato et al, Yogyo-Kyokai-Shi 11 (2), 1969, no
month..
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Primary Examiner: Bos; Steven
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch
Parent Case Text
This application is a continuation, of application Ser. No.
07/991,753, filed on Dec. 17, 1992, now abandoned.
Claims
What is claimed is:
1. A process for the production of a transition alumina having a
BET specific surface area of greater than 400 m.sup.2 /gram,
comprising thermally decomposing an aluminum sulfate under an
atmosphere comprising a reducing substance selected from the group
consisting of hydrogen, ammonia, propane and a propane mixture, in
an amount sufficient to reduce the aluminum sulfate to said
transition alumina at a temperature of about 500.degree. C. to
about 700.degree. C. and for a period of 0.5 seconds to about 15
hours.
2. A process for the production of a transition alumina having a
BET specific surface area of greater than 400 m.sup.2 /gram,
comprising thermally decomposing an aluminum sulfate wherein the
aluminum sulfate is thermally decomposed under an atmosphere
comprising a reducing substance selected from the group consisting
of hydrogen, ammonia, propane and a propane mixture, in an amount
sufficient to reduce the aluminum sulfate to said transition
alumina at a temperature of about 200.degree. C. to about
700.degree. C. and for a period of 0.1 seconds to 24 hours.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the production of a
transition alumina having a larger specific surface area for
applications of, for example, desiccants, absorbents, catalysts and
catalyst supports.
2. Description of the Related Art
The transition alumina has been widely used for various
applications such as the desiccants, the absorbents, the catalysts
and the catalyst supports, and it is expected to be used for
further applications.
From view points of increase of an absorbent capacity for water or
an intended absorbed component and effective application of the
catalysts, the transition alumina used for the above applications
is required to have a larger specific surface area.
Conventionally known process for the production of the transition
alumina includes a process as described in Japanese Patent Kokoku
Publication No. 21319/1975 in which alumina hydroxide produced by
the Bayer's process is thermally decomposed in an air flow at an
elevated temperature, a process as described in Applied Catalysis,
Vol. 24, pp. 25-35, 1986 in which an aluminum salt or an aluminate
is hydrolyzed to produce an amorphous alumina gel and the resultant
alumina gel is calcined and a process as described in Ceramics,
Vol. 24, No. 11, pp. 1042-1047, 1989 in which an aluminum alkoxide
is hydrolyzed and calcined. The transition alumina produced by the
above processes has a specific surface area of not larger than 350
m.sup.2 /g.
Even a commercially available transition alumina having the largest
specific surface area has a specific surface area of about 340
m.sup.2 /g as described in Table 11.25 of Chemical Society of
Japan, Chemical Handbook-Applied Chemistry II (Materials), 3rd ed.,
Maruzen, Tokyo, p. 865.
On the other hand, a process for the production of the transition
alumina in which an aluminum sulfate is thermally decomposed is
known from, for example, Japanese Patent Kokoku Publication No.
16934/1967, Yogyo Kyokai Shi (J. Ceram. Ass. Jpn.), Vol. 77, No. 2,
pp. 60-65, 1969 and Gendai-Kagaku-Koza 18, Inorganic Synthetic
Chemistry II, Kyoritsu-Shuppan, Tokyo, p. 113.
Gendai-Kagaku-Koza 18, Inorganic Synthetic Chemistry II, p. 113
describes that the alumina produced by the process described
therein comprising thermal decomposition at a temperature of about
900 .degree. C. has a specific surface area of about 170 m.sup.2
/g.
SUMMARY OF THE INVENTION
In view of the above prior art, the present inventors have made
extensive studies in order to find a process for the production of
the transition alumina having a larger specific surface area which
is economically produced in an industrial scale, and surprisingly
have found that the transition alumina having the larger specific
surface area as a BET specific surface area is produced when an
aluminum sulfate is thermally decomposed under a specific
atmosphere even at a relatively low temperature.
Thus, the present invention provides a process for the production
of a transition alumina by thermally decomposing an aluminum
sulfate characterized in that the thermal decomposition is carried
out under an atmosphere comprising a reducing substance.
DETAILED DESCRIPTION OF THE INVENTION
The present process will be, hereinafter, described in detail.
An aluminum sulfate used in the present invention is not
specifically limited, and is a commercially available aluminum
sulfate in the form of a solid or a solution which is generally
expressed by a following general formula:
wherein n is between 0 and 27. A basic aluminum sulfate or a basic
aluminum sulfate salt may be also used.
In addition to the aluminum sulfate, other aluminum salt such as
aluminum chloride, aluminum nitrate, aluminum formate, aluminum
lactate and aluminum acetate, an alumina hydrate or an aluminum
alkoxide may be combined provided that it does not cause remarkable
reduction of the specific surface area of the produced transition
alumina on the thermal decomposition.
In the case in which an aqueous aluminum sulfate solution is used
as a starting material, when the aluminum sulfate is thermally
decomposed, the aluminum sulfate solution may be heated under a
reducing atmosphere from the beginning of the heating.
Alternatively, the solution may be dried under any atmosphere
before the reductive thermal decomposition of the aluminum sulfate.
Namely, the solution may be heating dried under an oxidizing
atmosphere, a reducing atmosphere or an inert atmosphere.
Any manner for the drying may be used. Thus, a known manner may be
applied using, for example, an oven, an oil bath, a spray dryer, a
fluidized bed dryer, a vacuum dryer, a kneader, a ribbon dryer or a
paddle dryer. A drying temperature is not particularly limited, and
it is usually not less than about 100.degree. C. and lower than a
thermal decomposition temperature of the aluminum sulfate.
A temperature at which the thermal decomposition treatment of the
aluminum sulfate takes place under the reducing atmosphere is
higher than the thermal decomposition temperature of the aluminum
sulfate under the reducing atmosphere, but not higher than a
transition temperature at which produced transition alumina is
crystal transferred to .alpha.-alumina under the reducing
atmosphere. Concretely, the thermal decomposition treatment is
carried out under the atmosphere comprising the reducing substance
at a temperature of about 200.degree. C.-about 800.degree. C. for a
period of 0.1 sec.-24 hours, and preferably at a temperature of
about 500.degree. C.-about 700.degree. C. for a period of 0.5
sec.-about 15 hours.
The reducing substance may be any substance provided that it
reduces the aluminum sulfate, and it may be in the form of a gas or
a solid. For example, hydrogen, ammonia, a hydrocarbon having
carbon atoms of 3-4 such as propane, propylene, butene and butane,
carbon monoxide, urea, melamine, cyanuric acid and biuret can be
used. Especially, hydrogen, ammonia, propane or a propane mixture
such as a liquefied petroleum gas (LPG) is recommendable from view
points of its availability and ease of handling.
The reducing substance should be present in an amount which
sufficiently reduces the aluminum sulfate so that the transition
alumina is formed. The atmosphere under which the thermal
decomposition treatment of the alumina sulfate is carried out may
consist essentially of the reducing substance or it may be diluted
with an inert gas such as nitrogen. Alternatively, the atmosphere
during the thermal decomposition may comprise oxygen, and thus air
may be combined with the atmosphere. When the atmosphere contains
oxygen, an additional amount of the reducing substance is required
in addition to the sufficient amount for the reduction of aluminum
sulfate. The amount should be equal to or larger than a
stoichiometric amount to completely consume oxygen. It is of course
that oxygen should be present outside of an explosion range.
The transition alumina herein used is intended to mean an alumina
which is usually referred to as "transition alumina" by those
skilled in the art and which is a precursor on the way to
.alpha.-alumina when an aluminum hydroxide is heated. Concretely,
the transition alumina includes one which has a crystal form of
.gamma., .delta., .eta., .theta., .kappa., .rho. or .chi., and
especially one in the crystal form of .delta., .theta. or
.gamma..
When the present process is carried out, a stabilizer such as a
barium compound or a rare earth compound may be beforehand added to
the aluminum sulfate for the improvement of heat resistance and/or
a catalyst component such as a noble metal may be also beforehand
added to the aluminum sulfate.
Any known manner is employed for the reductive thermal
decomposition treatment of the aluminum sulfate. For example, a
rotary kiln, instantaneous calcination, fluidized bed calcination,
fixed bed calcination, a tunnel kiln, a batch furnace or a holding
furnace may be used for the decomposition.
The alumina after the reductive decomposition treatment may be the
transition alumina having a desired crystal form when thermal
decomposition conditions such as a temperature and a period are
selected properly. Alternatively, the alumina after the reductive
decomposition treatment may be calcined separately so as to have
the transition alumina having the desired crystal form.
The transition alumina so produced has a remarkably larger BET
specific surface area usually more than about 400 m.sup.2 /g,
typically more than about 450 m.sup.2 /g, and it may be used, as it
is or after ground, as catalyst supports or fillers for resins,
starting materials in the form of various types of desiccants,
absorbents, catalysts or catalyst supports or catalyst supports
coated on a surface of ready-made moldings such as a ceramic
honeycomb.
As described above, the present invention provides the economical
and simple process for the production of the transition alumina
having the larger specific surface area previously unknown in which
a cheap starting material such as an aluminum sulfate is used and
the thermal decomposition is carried out under the atmosphere
comprising the reducing substance at the relatively low
temperature. Thus, the present invention is very valuable in its
industrial point.
EXAMPLES
The present process will be, hereinafter, described in detail with
reference to Examples, but the present invention is not limited by
the following Examples.
Example 1
5 Grams of an aluminum sulfate (Al.sub.2 (SO.sub.4).sub.3.16H.sub.2
O) having a reagent grade was charged in a U-shaped tube made of
quartz glass having an internal volume of 100 ml. Hydrogen gas
having a purity of 100 % was supplied from one end of the U-shaped
tube at a flow rate of 200 Ncc/min. and an exhaust gas was purged
from the other end of the tube. Then, the alumina sulfate contained
in the tube was heated from a room temperature to a temperature of
550.degree. C. at a temperature increasing rate of about
250.degree. C./hour while hydrogen is supplied at the flow rate and
kept at a temperature of 550.degree. C. for 4 hours to thermally
and reductively decompose the aluminum sulfate to produce a
transition alumina (most of which was found to be .gamma.-alumina
by X-ray diffractometry). The resultant transition alumina had a
specific surface area of 452 m.sup.2 /g measured by the BET
method.
Examples 2 and 3
Two sets of the substance and the apparatus having the same
conditions as in Example 1 were prepared and the aluminum sulfate
was heated to a temperature of 600.degree. C. (Example 2) or
650.degree. C. (Example 3) and kept at the temperature for 4 hours
while hydrogen was supplied as in Example 1, whereby the aluminum
sulfate was thermally and reductively decomposed to the transition
alumina (most of which was found to be .gamma.-alumina by the X-ray
diffractometry). When the specific surface area of the resultant
transition alumina was measured as in Example 1 and found to have a
specific surface area of 563 m.sup.2 /g (Example 2) or 480 m.sup.2
/g (Example 3).
Comparative Examples 1-3
Three sets of the same substance and the same apparatus as used in
Example 1 was prepared and air was supplied in place of hydrogen in
the procedure of Example 1. The substances were heated to
temperatures of 500.degree. C. (Comparative Example 1), 800.degree.
C. (Comparative Example 2) and 1000.degree. C. (Comparative Example
3) and then kept at their temperature for 5 hours, respectively
while the air was supplied, whereby the alumina sulfate was
thermally decomposed to produce the transition alumina. The
resultant transition alumina had a specific surface areas of 5
m.sup.2 /g (Comparative Example 1), 50 m.sup.2 /g (Comparative
Example 2) and 120 m.sup.2 /g (Comparative Example 3),
respectively.
Example 4
Using the same substance and the same apparatus as in Example 1,
the transition alumina was produced with heating the substance to a
temperature of 600.degree. C. and keeping the temperature for 4
hours while supplying a liquefied petroleum gas (containing 99% by
volume of propane) at a flow rate of 200 Ncc/min. at a normal
pressure. The resultant transition alumina (most of which was found
to be .gamma.-alumina by the X-ray diffractometry) had a specific
surface area of 436 m.sup.2 /g.
Example 5
Using the same substance and the same apparatus as in Example 1,
the transition alumina was produced with heating the substance to a
temperature of 620.degree. C. and keeping the temperature for 4
hours while supplying ammonia gas at a flow rate of 200 Ncc/min.
The resultant transition alumina (most of which was found to be
.gamma.-alumina by the X-ray diffractometry) had a specific surface
area of 410 m.sup.2 /g.
* * * * *